Stop Fess and then install RPM/DEB package, see Installation in Installation Guide.

Fess 11 requires Elasticsearch 5.1 or the above, and indices for Fess 11 is not compatible with Fess 10.x. To upgrade to Elasticsearch 5, remove old indices and then upgrade Elasticsearch package. For Elasticsearch plugins, if you upgrade Elasticsearch, re-install all Elasticsearch plugins for the proper Elasticsearch version.